Digital processing of images has been studied in recent years. Various systems for recording digital image data with magnetic recording/reproducing apparatus (referred to as a VCR, hereafter) have been also studied. In general, when video signals are digitized, the amount of information becomes enormous and the transmission or recording, etc. of information without compression is difficult from the aspects of communication speed and expenses, etc.
Because of the above, image compression technology is indispensable in the transmission or recording of digital video signals and various drafts of standards have been examined in recent years. The MPEG (Moving Picture Experts Group) system has been standardized for moving pictures. In this MPEG system, video signals are encoded using a combination of DTC (Discrete Cosine Transform) conversion, inter-frame predictive encoding, run-length encoding and entropy encoding. That is, in the MPEG system, video signals are not only compressed in one frame by DCT (the intra-frame compression), but also inter-frame compression for reduction of redundancy in the time axis direction using the inter-frame correlation is adopted. Inter-frame compression further reduces bit rate by encoding a difference between two successive frames utilizing the nature of general moving pictures that they resemble closely in the preceding and succeeding frames. In particular, motion compensated inter-frame predictive encoding for reducing predictive error by obtaining an inter-frame error by predicting the motion of a picture is effective.
A helical scanning type VCR reads information recorded on a magnetic tape by tracing the recording tracks formed on the magnetic tape by the rotary drum heads. In normal reproduction, the head tracing agrees with the recording tracks and no special problem is produced. However, in high speed reproduction, the head traces the recording tracks while crossing them. Accordingly, in high speed reproduction only information recorded on such portions wherein each head agrees with the recording track azimuth. Even in this case, in an analog recording where positions on a picture correspond to the recorded positions on a recording medium, it is possible to reproduce one frame.
However, if the amount of encoded intra-frame compression frames and inter-frames compression frames differ and image data compressed according to the MPEG system is recorded on a recording medium, the vertical position of the image data on the picture does not correspond to the vertical recording position on a recording medium and it is not necessarily possible to reproduce one frame from reproduced data in the high speed reproduction. Furthermore, since the inter-frame compressed data cannot be decoded from a single individual frame, reproduction may become impossible if the same frames are unable to be decoded in the high-speed reproduction.
So, in the specification of the Japanese Patent Application (TOKU-GAN-HEI) No. 6-065298 previously filed by the applicant of this patent application, a method for intermittently recording data for high-speed reproduction at track positions (hereinafter referred to as a special reproduction data position) through which the heads run across them in high-speed reproduction is proposed. During reproduction, high-speed special reproduction images are obtained by accurately tracing the data positions whereon the high speed special reproduction data are recorded. For instance, to enable four-times speed mode reproduction, important data are to be recorded on special reproduction data positions from where a sufficient envelope level is obtained in the four-times speed mode reproduction.
In the proposal described above, three kinds of signals of frequency f0, f1, f2 (hereinafter referred to as pilot signals f0, f1, f2) are used as pilot signals for tracking and the pilot signals f1, f0, f2, f0, f1, f0, f2, f0, . . . are recorded on each track by superposing them in that order. During reproduction, levels of the pilot signals f1, f2, f3 contained in reproduced signals are compared and so controlled that the compared levels match with each other, that is, to agree the track phase with the tracks on which the pilot signal f0 is superposed. In this case, it is possible to match the track phase with the track of the pilot signal f0 every four tracks if the shifting direction of track phase is considered.
It is possible to match the track phase with a track of the pilot signal f0 even in, high-speed mode reproduction Therefore, the trace line of the head in high-speed mode reproduction is decided according to the tracks of the pilot signal f0. By recording high-speed mode reproduction data on the thus decided trace line, high-speed mode reproduction is enabled.
In high-speed mode reproduction, the heads of the same azimuth will trace across two times of given special reproduction speed number of tracks. Accordingly, it is better to record data next to that data recorded on the specified special reproduction data position in the same positions on following tracks after the two times of the specific reproduction speed number of tracks. Further, the heads trace the same azimuth tracks by every four tracks. Therefore, making sure to reproduce data even when the trace is carried out at any portion on the two times of special speed number of tracks (hereinafter referred to as a repetitive recording area), it is necessary to repetitively record the same data on four tracks in the repetitive recording area.
FIG. 8 is an explanatory diagram for explaining the recording on the special reproduction data position.
In FIG. 8, assuming that tracks run in the vertical direction, the special reproduction data positions on each track are given by square symbols. The arrows in FIG. 8 show the trace lines by the same azimuth head in the four-times speed mode reproduction. As described above, the same data is recorded on the same position in each track of every four tracks in the repetitive recording area and as the trace lines cross the four tracks in the four-times speed mode reproduction, four pieces of data can be recorded on the special reproduction data positions in one repetitive recording area. That is, in FIG. 8 the special reproduction data position is provided to every track so that data can be reproduced from four special reproduction data positions on four tracks by one trace. For instance, as shown in FIG. 8, frames 0 through 3 are recorded in the repetitive recording area A0 and data 4 through 7 are recorded in the repetitive recording area A1.
In the repetitive recording area A1, data 5, 6 and 7 are reproduced along the trace line T1, while data 4 is reproduced along the trace line T2. When rearranging the reproduced data in order of data 5, 6, 7 and 4, the original data 4, 5, 6 and 7 can be restored. For facilitating this rearrangement, a positional sequence signal is added to each data. Figures at the sides of the square symbols in FIG. 8 show the positional sequence signals.
That is, frame data with the positional sequence signals 0, 5, 6 and 7 are sequentially reproduced along the trace line T1. While, frame data with the positional sequence signals 4, 9, 10 and 11 are sequentially reproduced along the trace line T2. FIG. 9 shows the positional sequence signals of reproduction data that are sequentially reproduced for each trace. As shown in FIG. 9(a), the positional sequences of the reproduction data by the traces around the repetitive recording area A1 have the order of . . . 1, 2, 3, 0, 5, 6, 7, 4, 9, 10, 11, 8, 12 . . . . When this reproduction data train is rearranged in order of the positional sequence signals, the reproduction data in the original data sequence can be obtained as shown in FIG. 9 (b).
Further, considering the reverse reproduction, a frame-change flag showing the frame change is also recorded. That is, in the reverse reproduction it is necessary to reproduce data in a frame in the positive sequence while reproduce them in unit of frame in the reverse sequence. Therefore, a frame-change flag is used to restore reproduction data in unit of frame. FIG. 9(b) shows that the frame-change flags are at the same level and there is no frame change.
Further, considering that data around the frame ends are recorded on mid-tracks or end-tracks in the repetitive recording area, the positional sequence signal is initialized at the timing of the frame change given by the frame-change flag.
By the way, in the MPEG system, etc. a relatively large data storage is normally needed for recording data for one frame and a plurality of repetitive recording areas are needed for recording one frame. However, in the progressive refresh system disclosed in the literature "Grand Alliance HDTV System Specification" submitted to the ACATS Technical Subgroup; 2, 22, 1994, pictures are updated in unit of slice of the MPEG data. Therefore, when this system is adopted, the amount of data in one frame of the special reproduction data becomes relatively small and the frame changes may be frequent.
However, there was a problem in this case that the data rearrangement could not be made properly. FIG. 10 is a diagram for explaining this problem.
In FIG. 10 it is also assumed that the tracks run in the vertical direction and the special reproduction data portion on each track is given by the squares. Further, the special reproduction data positions shown by the thick square symbol indicates that data at the top of frame (the frame starting point data) are recorded and numerals in the squares show the frame numbers. Further, figures at the sides of the squares show the positional sequence signals. In FIG. 10, the 0-th through the fourth frame data are recorded in repetitive recording areas A0 to A2.
As shown in FIG. 10, three special reproduction data positions except the special reproduction data positions at the lowest end of the repetitive recording area A0 and the lowest end of the repetitive recording area A1 are traced along the trace line T1. Further, three special reproduction data positions except the special reproduction data position at the lowest end of the repetitive recording area A1 and the lowest end of the repetitive recording area A2 are traced along the trace line T2. The frame starting point data given by the thick square symbol is set to 0 since the positional sequence signal was initialized.
FIG. 11 (a) shows the reproduction data train obtained from the trains. The positional sequence signals of the reproduction data to be reproduced sequentially along the trace line T1 are 1, 0, 1, 2, respectively. The positional sequence signals of the reproduction data to be sequentially reproduced along the trace line T2 are 0, 1, 0, 1, respectively. FIG. 11(b) shows the frame numbers of these reproduction data. As shown in FIG. 11 (c), the positional sequence signal of the first reproduction data along trace line T1 is 1, this data is arranged before the reproduction data of the upper three special reproduction data positions on the repetitive recording area A0 and the reproduction data of the 0-th frame is properly arranged.
However, other positional sequence signals are arranged in the properly sequence as shown in FIG. 11 (a), and the reproduction data can not be rearranged. That is, the reproduction data of the first frame reproduced along trace line T2 is arranged between the last reproduction data of the second frame and the reproduction data of the third frame. Similarly, the third reproduction data by trace line T2 is the fourth frame data, but since the positional sequence signal is 0, it is arranged before the first data (the positional sequence signal in 0) of the third frame that is first reproduced by the next trace (not shown).
Thus, in a conventional method for rearranging special reproduction data using frame-change flags and positional sequence signals that are initialized at the changing point of frame-change flags, there was such a problem that data may not be rearranged properly if the amount of data of special reproduction data for one frame is small.